16 Printed Circuit Board (PCB) Reliability Test Methods

PCB has been playing a major role in electronics today. It is the primary part of any electronic component. Thus, the major concern is PCB quality, which is crucial, without a doubt. Optimal and accurate PCB design requires following guidelines and standards when considering the world of PCB design. Testing and simulating the product is still necessary to ensure that it performs as intended over a specified period and is reliable. It is necessary to perform these tests to assess the PCB's performance, reliability, and accuracy. The quality of PCB is inspected through various reliability tests. This article provides all the required and important PCB reliability test, their test principles, and their processes. 

Why PCB Reliability?

Schematics and hardware designs are the starting point for reliability tests. It is based on the properties of components and their placement in circuit designs. 

This test checks the potential issues of the solder joint, functionality issues, and short circuits of the board. All the PCB test helps to improve the reliability of the PCB and also helps to improve the functionality and design of the PCB. 

Overall, the reliability test offers various benefits:

• Finds errors and improves quality: Any PCB design's goals are performance and functionality. Thus, it should find errors and bugs as soon as possible. It increases the reliability of the PCB. 
• Cost reduction: Troubleshooting errors and faults save cost and further prevents risk or reliability in the future. 
• Increase Product Life: A reliability test can identify the lifespan of the PCB. Besides, it helps to identify the factors affecting the lifespan of a product. That information can improve the product design and help identify a product's lifespan. This will help achieve a longer and more sustainable product lifespan, adding greater customer value.
• Compliance with standards: A reliability test can help to ensure the product meets the standards reducing the risk of fines for the companies.

PCB Reliability Test

#1 Solder Mask Hardness Testing

The solder Mask Hardness test is one of the quality control tests on PCB. It determines the adhesion and hardness of the solder mask layer. This testing is important because the solder mask layer protects the PCB traces. It then prevents solder bridges from forming between adjacent components during the soldering process.

This testing aims to ensure that the solder mask is hard enough. The poor solder mask layer can crack off during the operation and lead to electrical failures. 

Test Principle

The test principle involves applying controlled pressure to a small area of the solder mask layer using a hardness test pen. The hardness tester measures the resistance of the solder mask layer to indentation and deformation. It indicates the hardness and adhesion strength of the layer. The standard test pencil hardness grade is ordered as follows: 

4B>3B>2B>B>HB>F>H>2H>3H>4H>5H>6H

The minimum harness for this solder mask testing should be greater than 6H. 

Testing Process

The basic testing process of this hardness test includes the following:

• Initially, place the board on a flat surface.
• Draw a harness range on the PCB board and look for the scratches using a standard test pen. Draw the line until there are no scratches. 
• Then finally, record the minimum hardness of the pencil. Make sure that the minimum hardness of this solder testing should be greater than 6H.

#2 Ionic Contamination Test

This reliability test is performed on electronic assemblies that erect the presence of ionic contaminants. The presence of ions can impact the reliability and performance of the assembly. The major purpose of this test is to ensure the board is free from ionic contaminations, as it can cause electrical shorts, corrosion, and many other failures.

It is tested through an Ion pollution machine: By detecting the number of ions per unit surface area of the sample, it can be judged whether the cleanliness of the sample meets the requirements.

Test Principle

The test principle involves immersing the electronic assembly in a test solution that dissolves any ionic contaminants present on the surface. The contaminants are then transferred to the test solution, and their concentration is measured using a conductivity meter or ion chromatography. The results are compared to specified acceptance criteria. It then determines whether the assembly meets the required level of cleanliness.

Test Method

• First, clean the surface of the samples with the use of 75% concentrated propanol. Propanol is chosen as ions can dissolve into it. Furthermore, it can also change its conductivity of it. 
• Then measure the contraction of ions with the use of the conductivity meter. 
• Compare the result with the specified acceptance for determining the level of cleanliness.
• Finally, record the result for future reference. 

The criteria for this ionic test is that the ion concentration should be 6.45 ug.NaCl/sq.in.

#3 Curing Test

The curing test measures the chemical attack resistance of resistive film/character. In the curing process, the materials are exposed to various energy sources and chemicals like dichloromethane to check the adhesion strength properties. The test helps to ensure proper cured material to achieve desired curing properties like adhesion and mechanical strength. 

Test Principle 

Curing reliability tests are based on the idea that the time and temperature of the curing process can affect the properties of a material. The material is exposed to different time and temperature combinations to determine the optimal curing conditions.

Test Method

• Use a dropper to drop an appropriate amount of dichloromethane onto the surface of the sample.
• Immediately test the tested part of the sample with a white cotton cloth.
• Observe the cotton cloth and the sample layout and make records.

For an effective result, ensure there is no solder mask or silkscreen on the white cotton cloth and no discoloration of the solder mask and characters on the layout.

#4 Thermal Stress Test

It is the reliability test on PCB that evaluates the ability of the base material and copper to withstand the change in temperatures. The major purpose of this test is to ensure that the electronic components can function under various thermal stress as they can physically damage the components over time. 

The reliability test involves the board subject to a temperate ranging from -65°C to +125°C. The components are heated and cooled over a specific period. The thermal stress of the base materials and the copper is monitored and controlled during this test. 

Test Method

The reliability test method for this thermal stress includes:

• Initially, bake the plate at 140°C for about 4 hours.
• Then, gently remove the plate and let it cool at room temperature.
• Take the sample out after 10 seconds and adjust the temperature of the constant temperature tin furnace to 288°C.
• Again, cool it to room temperature
• Finally, repeat the steps of the tin floating and cooling as required.

#5 Tg value test (Glass Transition temperature)

The major aim of this Glass Transition Temperature test is to examine the glass transition temperature of the board. This TG value test can be performed using differential scanning calorimetry and thermomechanical analysis. The thermomechanical analysis has the better ability to produce highly accurate measurements. 

Test Methods

• First, prepare the sample. The sample should be a small amount of material, typically 15-20mg.
• Then, bake the sample at 105 degrees C for 2 hours. Then finally, put them in the dryer to cool to room temperature.
• Put the sample in the sample stage in the DSC tester. Then, set the temperature increase rate at 20℃/min.
• Finally, scan it two times and record the Tg.
• Make sure that the Tg should be above 150 degrees C.

#6 Solderability Test

Solderability testing is a method that inspects the solderability of the solder pads and the through holes on the board. It is an important process in electronics manufacturing to ensure that components can be effectively soldered onto a printed circuit board (PCB). It uses equipment like a solder machine, oven, and timer to carry out this solder test. The solderability test ensures the PCB surface is properly prepared for soldering, and thus it forms a long-lasting and strong bond with the solder.

Solderability tests can be performed using several methods, including dip-and-look, wetting balance, and solder paste. A dip-and-look test determines the quality of a solder joint by dipping the component into molten solder. When wetting balance testing is performed, a small amount of solder paste is applied to the component before it is heated. It then determines the quality of the solder joint.

Test Method

The basic solderability testing method includes the following:

• Initially, bake the board in the oven at 105 degrees C for about 1 hour.
• Dip the flux.
• In the solder machine, place the board flat, and immerse it at 235°C for 3 seconds, then remove it and check for tin dips on the solder pads.
• Finally, check the through holes if they dip tin by vertically placing the board into the solder machine at 235°C for 3 seconds and taking it out afterward.

#7 PCB Peel Test

PCB peel reliability test measures the peel strength of rigid printed boards under normal test atmospheric conditions. The test involves applying a tensile force to a portion of the PCB. It then causes the separation between the layers and measures the force required to do so.

Test Purpose

The PCB peel test aims to evaluate the adhesion strength between the layers of a multilayer PCB. The test helps to ensure that the layers of the PCB are properly bonded and have sufficient adhesion strength to prevent delamination or separation during use.

Test Method

• Peel one end of the printed wire on the sample from the base material at least 10mm. The finished printed board's length is not less than 75mm, and the width is not less than 0.8mm.
• Fix the sample on the peel tester, and use The clamp to clamp the wire.
• Peel off the printed wire with a uniformly increased tensile force perpendicular to the sample. If the stripped length is less than 25mm, it will break, and the experiment will be repeated.
• Record the anti-stripping force and calculate it per millimeter of width. Peel resistance (i.e., peel strength).

During this test, the wire stripping strength should be at least 1.1N/mm.

#8 Voltage Withstand Test

As the name suggests, it tests the voltage withstand ability of the board. It makes use of the voltage tester. The Voltage Withstand Test evaluates a component's ability to withstand electrical stress without damage. This is important for ensuring the safety and reliability of the product.

Test Principle

The principle of the Voltage Withstand Test is relatively simple. A product or component is connected to a high-voltage source and subjected to a specified voltage level for a set period. The test is designed to simulate the electrical stress that the product or component is expected to encounter during normal operation and to ensure that it can withstand it without any electrical breakdown or damage.

Test Method

• Initially, properly clean and dry the sample.
• Then, connect the +/- terminals of the withstand voltage tester to one end of the conductor to be tested.
• Finally, the recording shouldn’t exceed 100V/s. The duration is 30s under the voltage of 500VDC.

#9 CTE Test

CTE test determines the Coefficient of Thermal Expansion test of a material. Thus determines the extent to which a material expands and contracts when subjected to changing temperatures. CTE test is applicable in the electronics, aerospace, and automotive industries. Then, it ensures that the components and materials can withstand the stress of the temperature change. 

Test Principle

CTE test measures the length of the materials with the temperature change. It uses equipment like Thermal Mechanical Analysis (TMA) tester, dryer, and oven. 

Test Method

• Initially, take a sample and polish the edge of the sample to be smooth. The sample size is 6.35*6.35mm.
• Then, put the sample in an oven at 105°C for 2 hours, take it out, and put it in a desiccator to cool to room temperature for at least 30 minutes.
• Then, put the sample on the sample stage of TMA, set the temperature rise rate to 10°C/min, and set the scan termination temperature to 250°C.
• Finally, record the CTE before and after the Tg point.

#10 Explosion Test

The explosion testing method assesses the degree of the internal heat of PCB substrates. 

This test aims to ensure that the PCBs can pass the explosive test without failure. It is crucial for safety in the military, aerospace, and mining applications.

Test Method

PCB substrate undergoes an explosion test through the following process:

• Initially, take a sample and polish the edge of the sample to be smooth. The sample size is 6.35*6.35mm.
• Then, put the sample to be tested in an oven at 105°C for 2 hours, take it out, and put it in a desiccator to cool to room temperature for at least 30 minutes.
• Then, put the sample on the TMA sample stage, set the probe pressure to 0.005N, and the heating rate to 10°C/min.
• Furthermore, raise the sample temperature to 260°C. When the temperature rises to 260°C, keep the temperature constant for 60 minutes, Or stop scanning until the test is overdue.
• When obvious stratification occurs, stop scanning.
• Finally, explosion time is defined as the time from constant temperature to obvious stratification. Record this time.

#11 Solder Mask Dissolution Test

It tests whether the solder resist paint on the sample's surface has been hardened enough to cope with the heat generated during welding. This test helps to determine the reliability and durability of the solder mask. 

Test Principle

The solder mask dissolution testing principle involves immersing the PCB in a chemical or solvent for a specified period. Then observing any changes to the solder mask is the next step. The test measures the ability of the solder mask to resist damage or degradation when exposed to chemicals or solvents, which can cause the mask to soften, blister, or delaminate.

Test Method

• Initially, drop a few drops of chloroform on the surface of the solder resist paint of the sample and wait for about one minute.
• Use a rag to wipe off the dripped chloroform, and the surface of the cloth should have no color attached to the solder resist paint.
• Finally, use your nails to scrape off at the same position.

#12 Lead-free Solderability Test

The major aim of this lead-free solderability test is to predict the soldering condition of the products handled by the customer. For this, it uses a Solder pot to simulate the soldering condition of the customer. Furthermore, it uses an oven, lead-free solder pot, stopwatch, lead-free flux, and 10x magnifying glass.

The test helps to ensure that the components and PCB can be effectively soldered using lead-free solder.

Test Method

• Select an appropriate sample. The BGA and CPU have not been drawn with a whiteboard marker, and after confirming that the sample's surface is clean, put it into the oven and bake at 123°C for one hour. After removing the sample, let it cool down to room temperature.
• Put the flux on the sample completely, and the sample must drip upright for 5~10 seconds so that the excess flux can drip back.
• Place the drop sample carefully on the surface of the tin pool with a temperature of 260°C, and float for 3-5 seconds.
• Wear high-temperature-resistant gloves, sleeves, and protective masks during operation, and use long handles to pick and place samples and conduct experiments.

#13 Impedance Test

Impedance test measures whether the impedance value meets the requirements or not. And it uses the impedance tester for this purpose. 

Resistance, capacitance, and inductance are encountered by an electrical signal traveling through a trace or plane when it encounters impedance testing. In addition to the material properties, and dimensions, the impedance of the trace or plane is affected.

It tests according to the impedance testing machine operating standard.

#14 Hole-pull Test

The hole-pull test measures the tensile strength of plated hole copper. It is one of the mechanical tests that evaluate the quality of plates through the hole in the PCB. 

Test Principle

Plating quality on the PTH directly influences the adhesion between the plating and the substrate, which is the basis of the hole-pull test. A pin or wire is inserted into the PTH and pulled out to perform the test while measuring the force required. PTH adhesion strength determines the force needed to remove the wire from the PTH.

Test Process

• Insert the copper wire directly into the hole, and solder it firmly with an electric soldering iron. 
• The copper hole must have the PAD surface intact and cut off the excess line on the PAD side.
• Clamp the end of the copper wire with a tensile machine. Tighten it, press the tensile machine to rise until the copper wire is broken or the hole is pulled out, and count the reading C (Kg).
• Finally, use a vernier caliper to measure the inner diameter C2 (mm) of the hole and the outer diameter C1 (mm) of the annular ring.

Thus, manufacturers can ensure that the PTHs will not fail due to mechanical stress during use by testing the adhesion strength between the plating and the substrate material.

#15 High Voltage Insulation Test

It tests the insulation properties of circuit board materials. This test involves applying a high voltage to the board to determine if there are any failures or breakdowns. Thus,  it helps to ensure PCB insulates properly and can bear the operating voltage requirements without an electrical breakthrough. 

Test Method

• Initially, bake the board at a temperature of 50~60°C/3 hours, and cool to room temperature. Then select a pair of unconnected wires on the sample closest to each other. 
• Test according to the operation standard of the high-voltage insulation tester. The test requirements are 1. Line distance<3mil, required voltage 250V, current 0.5A 2. Line distance≥3mil, required voltage 500V, current 0.5A
• Finally, according to customer requirements, set the voltage and current 4. Or use 1000V for double-sided boards and 500V for multilayer boards

Then finally confirm the result by continuing to power on for 30 seconds, and if there is a breakdown phenomenon, the sample is unqualified. 

#16 Acid and Alkali Resistance Test

It evaluates the acid and alkali resistance of the Solder Mask. The test helps to ensure the quality of PCB when exposed to harsh environments. 

The manufacturer tested the PCB for acid and alkali resistance to determine whether they resist corrosion under acidic and alkaline conditions. Furthermore, in harsh chemical environments, the PCB must maintain its integrity and functionality. 

Test Process

• Initially, prepare 10% H₂SO₄ and 10% NaOH.
• Heat the samples in an oven to about 120±5°C for about 1 hour.
• Soak the two groups of samples in the above solutions for 30 minutes.
• Take out the sample and dry it, and stick it on the paint surface with adhesive tape about 2 inches long.
• Finally, wipe the adhesive tape three times by hand. Ensure that the adhesive tape is used once each time.

Comparison Among all the PCB Reliability Test

Conclusion

NextPCB undergoes a series of extensive inspections and tests at each step of the assembly process. We ensure our product meets the quality requirements. We check our PCB through all the required reliability tests before sending them to the customers. Feel free to contact us if you want to know more about our services and products.